This invention relates to a hydrodynamic bearing, and particularly to one useful as a driveshaft bearing of a thermal engine such as a Stirling cycle engine.
In one design of a Stirling engine, a swashplate is journaled for rotation within a housing. The swashplate is driven by crossheads connected to reciprocating pistons and the swashplate in turn rotates a driveshaft through which mechanical power is delivered to a load coupled to the engine. The construction of this type of drive mechanism is such that forces acting on the swashplate are radially positioned from the axis of rotation of the swashplate. The interaction of the drive mechanism with the swashplate is such that forces acting on the swashplate can be resolved into components producing rotation and components which impart a rotating bending load on the driveshaft.
The driveshaft of the above mentioned type of thermal engine is supported at displaced axial locations by bearings. The swashplate is carried by the unsupported shaft length between the bearings which is subjected to bending deflection caused by the rotating bending moment. The bearings must therefore accommodate a small degree of bending deflection of the driveshaft. Rolling element type bearings may be used which allow a predetermined range of angular displacement of the driveshaft. Although such bearings generally operate satisfactorily, they have a finite lifespan. As with any complex machine mechanism, it is desirable to minimize required maintenance and mechanical failures. Simple journal or plane hydrodynamic bearings have inherently long life capabilities. Typical plane bearings, however, do not accommodate angular displacement of a shaft journal with respect to the bearing. In view of the foregoing, there is a need to provide an improved bearing for supporting driveshafts of thermal engines, such as Stirling engines, which has the capability of accommodating rotating bending deflection of the driveshaft while providing long operational lifespan capabilities.
In accordance with the present invention, the above mentioned desirable features are obtained through the use of a plane hydrodynamic bearing forming a convex spherical surface having its center coincident with the axis of rotation of the driveshaft which is fitted within a bearing forming a complementary concave spherical surface. In accordance with a first embodiment of this invention, a spherical journal is rigidly affixed to and rotatable with the supported driveshaft. In accordance with a second embodiment of the invention, the driveshaft has a cylindrical journal which passes through a bearing member having a cylindrical inside bearing surface which supports the shaft journal, and a spherical outer surface which is closely received by a concave spherical bearing. Both embodiments accommodate slight axial "wobble" of the supported driveshaft. Lubrication of the bearing surface interfaces can be obtained through a splash-type or immersion system, or through pressurized lubrication feed.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.